You say you're "open to her exploring possibly being bi-sexual", but is she actually bisexual - as in interested in having a sexual relationship with a woman - or is that the only option currently open to her whether she likes girls or not?

No, she doesn't know if she identifies as bi-sexual, as she has had sex with women before, but has not been in a relationship with one before. She knows I am comfortable with her exploring that, but knows about my anxiety and fears with men. I haven't put any constraints on her, but have tried to express my feelings around it.